> I have measured values for 47 chemicals in a stream. After processing > the original data frame through reshape2, the recast data frame has this > structure: > > 'data.frame': 256 obs. of 47 variables: > $ site : Factor w/ 143 levels "BC-0.5","BC-1",..: 1 1 1 2 2 2 2 2 2 2... > $ sampdate : Date, format: "1996-04-19" "1996-05-21" ... > $ Acid : num NA NA NA NA NA NA NA NA NA NA ... ... > > I want a subset of this with only 7 chemicals: Ca, Cl, Cond, Mg, Na, SO4, > and TDS. The subset help page tells me that I can use a logical subset to > extract these 7 rows while keeping all columns, but I do not know how to > write that logical subset.
Wow, I don't see how you wound up with the code you tried based on the instructions. I guess for some of us the best instruction is a bloody nose, myself often included. It sounds like you want to get rid of some columns in the reshaped dataframe, not rows. new <- old[c('site', 'Ca', 'Cl', 'Cond', 'Mg', 'Na', 'SO4', 'TDS')] will work, as will the following if you insist on using the subset function. new <- subset(old, c(site, Ca, Cl, Cond, Mg, Na, SO4, TDS)) If you actually want to get rid of rows that aren't the minerals of interest, then work with your unreshaped dataframe: new <- subset(reallyOld, parameter in c('Ca', 'Cl', 'Cond', 'Mg', 'Na', 'SO4', 'TDS')) -- Curt Seeliger, Data Ranger Raytheon Information Services - Contractor to ORD seeliger.c...@epa.gov 541/754-4638 [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.